Endotracheal intubation is a core technique in anaesthesia (and critical care medicine). It is the gold standard method to provide oxygenation and ventilation to a patient under general anaesthesia. It requires the passage of an endotracheal tube (ETT) through the vocal cords into the trachea.
The primary and traditional method of endotracheal intubation involves direct laryngoscopy with a laryngoscope. The laryngoscope has a gently curved blade which is passed into the mouth and sits in the oropharynx to provide a direct line of sight to the vocal cords. Most patients can be successfully intubated using this technique; however circumstances where this is difficult or impossible occur relatively regularly in anaesthesia (6%) and other areas of critical care (16%).
Difficult intubation has the potential to result in great patient harm from inadequate oxygenation causing death, brain damage and/or heart attacks. Difficult intubation requiring multiple or repeated attempts can also result in trauma to the airway. Management of these scenarios has been and continues to be a major focus in anaesthesia and critical care medicine. This has resulted in multiple “airway” management strategies and the development of improved equipment.
Although there can be a variety of causes that result in a difficult intubation, ultimately there are two main factors that are responsible:                Difficulty in visualising the vocal cords and/or        Difficulty in directing an ETT through the vocal cords into the trachea.        
These two factors are generally managed by using a videolaryngoscope (to improve visualisation of the vocal cords) and/or a specialised ETT introducer (to guide the ETT through the vocal cords). However both of these techniques have limitations which can still result in a difficult or failed intubation for various reasons detailed below.
For the first factor, difficult visualisation, direct laryngoscopy relies on achieving a “line of sight” to directly visualise the vocal cords from the mouth and provide a pathway to pass the ETT. Certain patient factors or abnormal upper airway anatomy can make this “line of sight” difficult to achieve, and hence the intubation difficult. In current anaesthetic practice, this situation is most likely to be managed with a videolaryngoscope (VLS). This technology incorporates a light source and optical capabilities onto the tip of a modified laryngoscope. An image is produced that can be visualised on a separate monitor. This technique is called “indirect” laryngoscopy because it does not require a direct “line of sight” to visualise the vocal cords from the mouth. It can greatly improve the visualisation of the vocal cords in most patients with a difficult intubation. Many of the devices have a sharply angled curve on their VLS blade designed for abnormal airway anatomy. This effectively allows the anaesthetist to “see around corners” and has been an extremely valuable advancement in airway management.
For the second factor, difficulty in directing the ETT, successful intubation requires the ETT to travel along the pathway between the mouth and vocal cords into the trachea.
Referring to FIG. 1, good visualisation of the vocal cords during traditional direct laryngoscopy generally implies that there is a shallow (gently curved) pathway for the ETT to follow within the oropharynx and that intubation will be easy. This however may not be the case and despite good visualisation, the ETT cannot be directed through the vocal cords.
Poor visualisation of the vocal cords during direct laryngoscopy often means that there is a more sharply angled pathway that the ETT must follow in the oropharynx. This sharp angle of approach can make it impossible to direct an ETT through the vocal cords without using a specialised introducer.
When a VLS is used to improve a poor view of the vocal cords obtained with direct laryngoscopy, it is expected that the ETT must follow a very sharply angled pathway in the oropharynx. It is generally considered essential to use an introducer to negotiate this sharp angle. This is one of the limitations of the VLS (i.e., it gives a good view of the vocal cords, but makes it more difficult to pass the ETT).
Specialized introducers are designed to guide the ETT through the vocal cords. The introducers can be bent to fit the shape of the pathway required for intubation, thus increasing the chance of successful ETT placement. There are two main types of introducer: (a) stylet or (b) bougie. The stylet is placed within the lumen of the ETT before intubation and is used as a shaper or stiffener of the ETT. It functions as a single unit combined with the ETT during intubation and is then removed after the tip of the ETT enters the vocal cords. The bougie is used as a primary device which is passed through the vocal cords into the trachea. The ETT is then slid (railroaded) over the bougie to enter the trachea and the bougie is then removed through the ETT lumen. It functions as a conduit for the ETT and is more versatile than a stylet. It is a very important piece of equipment used to direct the ETT through the vocal cords during a difficult intubation.
The introducers have limitations and they can fail. Referring to FIGS. 2 and 3, when an introducer has to follow a very sharp angle of approach in the oropharynx, it can be very difficult to direct the tip through the vocal cords. The introducer can be bent into the shape of this sharp approach angle, however two force vectors need to be considered in determining successful placement. Force is applied along the longitudinal vector of the shaft of the introducer which needs to be transmitted to a vector plane aligned with the tip towards the vocal cords so it can advance. There is a certain oropharyngeal approach angle beyond which the force applied along the longitudinal vector will be unable to advance the tip in its required vector (i.e., pushing the introducer from the shaft will not advance a sharply bent distal tip through the vocal cords).
If an introducer is successfully directed through the vocal cords after following a sharp angle of approach, it can then become stuck against the anterior wall of the trachea immediately below the vocal cords. The lumen of the trachea follows another acute angle away from the approach direction of the introducer at the vocal cords. This can make it very difficult to direct the introducer or ETT into the trachea despite passing through the vocal cords. (See FIG. 5.) This can also result in a failed intubation. Some of the commonly used bougies have an anteriorly angulated “coude” tip (which is recommended) however this can increase the chance of becoming stuck against the anterior tracheal wall as described above when there is a sharp approach angle.
The more difficult it is to visualise the vocal cords and the sharper the approach angle to the vocal cords means it is more difficult to successfully use an introducer. The VLS is particularly susceptible to this type of failure in a difficult intubation scenario due to its non-“line of sight” view. A well recognised and commonly reported cause of difficult or failed intubation when using a VLS involves failure to direct the ETT or introducer into the vocal cords despite good visualisation. (See FIG. 4.)
Accordingly, there exists a need to provide an improved device less prone to problems such as those described above. The present invention seeks to lessen these problems by providing a device which allows the intubation of a patient without significant difficulties associated with conventional devices.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.